<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html{
            font-size: 30px;
        }
        #box1{
            font-size: 20px;
        }
        #box2{
            width: 100px;
            height: 100px;
            /* font-size: 10px; */
            background: lightseagreen;
            border-left: 2em solid lightsalmon;
            border-right: 1rem solid lightgreen;
        }
    </style>
</head>
<body>
    <div id="box1">
        <div id="box2"></div>
    </div>
</body>
</html>